The present invention relates to novel thermosetting compounds which hardly generate volatile by-products on curing, cured products thereof and a method for manufacturing the thermosetting compounds.
Thermosetting resins, such as phenolic resins, melamine resins, epoxy resins, unsaturated polyester resins and bis-maleimide resins, are widely used in many industrial fields due to the heat resistance originated from their thermosetting property and to their reliability. These resins however suffer their respective disadvantages, for example, the generation of volatile by-products on curing of phenolic resins or melamine resins, the poor inflammability of epoxy resins and unsaturated polyester resins and the extremely high price of bis-maleimide resins, and, in practical use, such disadvantages have unavoidably been tolerated depending on their uses. To solve this problem, there have been made attempts to develop novel thermosetting resins free from such disadvantages.
One of the attempts resulted in the development of dihydrobenzoxazine compounds (refer to the specification of Japanese Patent Unexamined Publication No. 49-47378 and the specification of U.S. Pat. No. 5,152,939). The compounds are cured by the ring-opening polymerization of the benzoxazine rings, to cause little generation of volatile matters on thermosetting.
However, the curing reaction brings about not so long extension of molecular chains (Polym. Sci. Technol., 31, p.27-49, 1985) and inadequate density of cross-linking, so that softening or thermal deterioration occurs over 200.degree. C.
It is also known that the ring-opening polymerization takes disadvantageously longer curing time as compared with the curing reaction of conventional phenolic resins, resulting in low productivity that limits the industrial use of the compounds.